The measurement of the energy of cosmic rays I—The electro-magnet and cloud chamber

Abstract

1—The Construction and Performance of the Electro-Magnet The energy of the cosmic ray particles has been determined from the curvature of their tracks in a strong magnetic field by Kunze, and by Anderson. Kunze used a power of 500 kw in a copper solenoid weighing 1100 kg to give a magnetic field of 18,400 gauss over a chamber 16⋅4 cm in diameter. Anderson used an electro-magnet with heavy water-cooled copper coils and a relatively light iron yoke. A power of 440 kw gave a field of 15,000 gauss over a chamber 16⋅5 cm in diameter, the actual length of the tracks photographed being about 12 cm. In order to obtain a similar performance without the use of such a very large amount of electric power, an electro-magnet has been constructed of a more conventional design, that is with an iron yoke which is heavy compared with the weight of the copper coils. The iron yoke weighs about 8000 kg and the copper coils 3000 kg. Figs. 1 a and 1 b show the detail of the design, and fig. 2 shows a photograph of the magnet in use with the cloud chamber and subsidiary apparatus. The diameter of the pole face is 25 cm, and the gap can be varied from 5 to 20 cm by sliding one pole piece along the baseplate by means of a screw.